The subject matter described herein relates generally to photoacoustic Doppler-based flowmetry and, more particularly, to detecting fluid flow in optically scattering media and/or low-speed blood flow of relatively deep microcirculation in biological tissue.
Laser flowmetry and acoustic flowmetry based on the Doppler effect have become valuable tools for fluid mechanics measurements. In addition, low-coherence optical Doppler tomography has been developed for similar applications. Each method requires the presence of small scattering tracer particles to provide detectable backscattering signals. In measurement of tissue blood flow, red blood cells may serve as endogenous scattering tracer particles. At least some known systems based on the photoacoustic Doppler effect use movement of a thermoacoustic array. However, such systems do not involve a flow medium. Rather, a laser beam was scanned over an absorbing liquid and, as a result, the Doppler shift depends on the laser scanning speed.